The manufacturing of laminates and other wood members having wood laminates bonded together is known. Many attempts have been made in the past to increase and to improve the consistency of the properties of the laminates. It has been found that wood members have a tendency to fail catastrophically on the tension surface of the wood member. More particularly, conventional practices of fabricating wood members include bonding a plurality of wood laminates together to form a single structural member wherein the wood laminates are bonded together by an adhesive and the laminates may be conforming to a predefined geometry such as a unidirectional pattern.
Wood members that are manufactured to prior art principles normally fail on the tension surfaces of the wood member when the applied deflection of the wood member generates an outer fiber stress that exceeds the critical stress required to initiate and propagate fracture failure at the site of either a defect in the wood member such as a knot or a manufacturing defect such as a joint used to longitudinally attach the wood laminates to one another.
When a conventional wood member is subjected to a downwardly directed load at, for example, the mid-point of the wood member, a lower half of the thickness of the member is subjected to tension stresses while the upper half of the thickness of the member is subjected to compression stresses. When a wood member fails in the tension zone, i.e. in the lower half of the member if the member is subjected to a downward load, the failure can be catastrophic. However, a failure in the compression zone, i.e. upper half of the wood member, is a more benign mode of failure. Substantial amounts of FRP reinforcing laminates, such as carbon, aramid and glass fibers can be added to the tension zone or the wood member to shift the location of the (load) failure from the tension zone to the compression zone. Unfortunately, the FRP reinforcing laminates are not only very expensive but the reinforced members may be very labor intensive to make. It has been shown that reinforced wood members are most likely to fail adjacent to wood laminate defects such as knots and at finger joints.
Attempts in the past have focused on shifting the neutral axis towards the tension zone to reduce the outer tension fibers stresses as compared to non-reinforced members that are subjected to the same loading. For example, U.S. Pat. No. 5,362,545 to Tingley describes a wood member that has a FRP reinforcing material added exclusively to the tension side of the member. The current reinforcement technologies require a significant amount of expensive high performance FRP fiber laminates which in turn substantially increases the cost of the final product. Another deficiency of the current reinforcing technology is that the variance of failure load is not significantly reduced compared to conventionally sawn lumber technology partly due to the adverse affects of joint strength variability. Therefore, there is a need for a less costly and more reliable reinforcing method-of-wood members.
According to the method of the present invention, and adhesive is applied to high strength fiber reinforcements and the first and second wood strands to bond them together so that they form a wood composite laminate. Before the adhesive is cured, a tension force is applied to the high strength fiber reinforcements and an equilibrium compression force is applied to the first and second wood strands. The adhesive is cured while maintaining the tension force to the high strength fiber reinforcements and the compression force to the wood strands. The prestressed wood composite laminate may be attached to the tension zone of a wood body. The wood body has a tension zone and a compression zone so that a neutral plane is disposed between the tension zone and the compression zone.